The present disclosure relates to fuel cell systems for the production of electricity. In particular, the present disclosure relates to a fuel cell system capable of capturing CO2 from a fuel cell.
Fuel cells are devices that are capable of converting chemical energy stored in a fuel, such as a hydrocarbon fuel, into electrical energy through electrochemical reactions. In general, a fuel cell comprises an anode, an electrolyte layer, and a cathode. The electrolyte layer serves to transfer ions between the anode and the cathode, which facilitate reactions within the anode and the cathode to generate electrons for the production of electricity.
Fuel cells are often characterized by the type of electrolyte layer used for the transfer of specific ions. For example, one type of fuel cell is the solid oxide fuel cell (SOFC), which incorporates a solid ceramic electrolyte for the transfer of negatively charged oxygen ions from the cathode to the anode.
During operation of an SOFC, air is supplied to the cathode where oxygen gas reacts with electrons to form negatively charged oxygen ions, which are transferred to the anode through the electrolyte layer. At the same time, a hydrocarbon fuel, such as natural gas, is mixed with steam in a reforming process where methane and water react to produce hydrogen gas and carbon dioxide. The hydrogen gas and carbon dioxide react with the oxygen ions transferred by the electrolyte layer, producing the electrons for electricity and completing the electrical circuit. As a byproduct of this reaction, water, carbon dioxide, and residual hydrogen gas are released as an exhaust from the anode. Part of the anode exhaust is typically recycled to the anode, but the remainder is exported to prevent excessive buildup of carbon dioxide.
Carbon dioxide, however, is considered to be a harmful emission due to its effect on climate change. Thus, in order to avoid the release of carbon dioxide into the environment, it is preferable to capture the CO2 from the anode exhaust and store the CO2 for other, more environmentally-friendly purposes, such as underground storage or oil production needs. One method to capture carbon dioxide from the anode exhaust of an SOFC is through the use of an anode gas oxidizer, which is fed pure oxygen instead of air, avoiding dilution of the CO2 with N2. An anode gas oxidizer uses oxygen gas to oxidize the anode exhaust in order to capture the heating value contained within the exported anode exhaust. However, the pure oxygen needed for this process can be expensive to produce. Currently, methods in generating pure oxygen for use in an anode gas oxidizer are limited to the use of an air separation unit, which separates oxygen from air to supply the oxygen needed. However, such a system is costly and inefficient. Thus, it would be advantageous to provide an efficient and cost-effective system that can provide the oxygen necessary to facilitate the capture of CO2 in the exported anode exhaust.